Coupling mechanism

ABSTRACT

A mechanism for clamping a tool (e.g. a probe) and a shank together comprises a clamping pin (144), which bears against an annular lip (142) in the rear face of the probe. A shaft (148) of the pin (144) extends into the shank (150), and two diametrically opposite, radially extending clamping bolts (160) supported by the shank (150), bears against a frusto-conical clamping surface (158). The action of the bolts (160) on the surfaces (158) urges the probe and shank together. The probe and shank are adjusted laterally relative to each other by four adjusting bolts (166) supported in the annular lip (142) which bear against a flange (152). The flange (152) is provided on the shank (150) and extends into the probe (140).

BACKGROUND OF THE INVENTION

The present invention relates to a coupling mechanism, which may be usedfor example, in coupling a tool to a shank for supporting the tool in ahead of a coordinate positioning machine, e.g. a machine tool orcoordinate measuring machine.

FIELD OF THE INVENTION

It is known to releasably couple a tool such as a probe or cutting tool(e.g. a boring bar) to a shank, which supports the tool in a machinetool. This enables replacement of a faulty, worn, or broken boring barfor example without replacement of the shank as well, and thus is morecost effective. However, releasable coupling mechanisms have thedisadvantage that, during coupling the axis of the too may be displacedby a small distance from the axis of the shank as a result of lateralforces in the coupling mechanism. This source of error is undesirable,and particularly so where the device to be coupled to the machine is atouch or other probe.

DESCRIPTION OF PRIOR ART

It is known, for example from EP 0125529, to fix a tool holder to thespindle of a machine tool, by mounting a clamping pin having a conicalrecess at one end in a transverse bore provided in a shaft on the toolholder. The shaft (and clamping pin) are then inserted into a bore inthe spindle, and a clamping screw extending radially into the bore isbrought into engagement with the conical recess, to urge the tool holderand spindle against each other. It is also known, from U.S. Pat. No.4,776,734 to attach a tool holder to a spindle fixture by axiallyextending screws. The axial alignment of the spindle fixture and toolholder is adjusted by a radially extending screw, carried in a rotatablering provided on the spindle fixture, which bears against the toolholder.

SUMMARY OF THE INVENTION

The present invention provides a mechanism for clamping a tool to ashank engageable with a spindle of a machine tool, the shank having anaxis, the mechanism comprising:

clamping means having:

a) means provided on one of the tool and shank for applying a force,radial with respect to the axis of the shank, on the other of the tooland shank;

b) means provided on the other of the tool and shank, and operable bythe radial force for producing a clamping force parallel to the axis toclamp the tool and shank together; and

adjusting means, distinct from the clamping means and provided on one ofthe tool and the shank for aligning, the tool and shank relative to eachother in a first direction transverse to said axis, and in a seconddirection transverse to both said first direction and said axis.

A second aspect of the present invention provides a coupling mechanismfor first and second parts of a tool comprising:

a projection provided on the first part and a recess provided on thesecond part for receiving the projection;

clamping means provided in the body of the second part for applying aforce to the projection;

means provided on the projection for causing the force to urge the firstand second parts together, thereby providing a resultant clamping forcefor the first and second parts; and

adjusting means, distinct from said clamping means and provided in thebody of the second part, for applying an adjusting force to theprojection in a direction substantially perpendicular to the resultantclamping force.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,and with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a touch probe attached to a shank;

FIG. 2 shows a section through a first embodiment of a couplingmechanism according to the present invention;

FIG. 3 shows a section through a second embodiment of a couplingmechanism according to the present invention;

FIG. 4 shows a section through a third type of coupling mechanismaccording to the present invention; and

FIG. 5 shows a section through a preferred coupling mechanism of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, a touch probe 10 carries a stylus 6 whichterminates in a spherical measuring tip 8 for contacting a workpiece.The probe 10 is releasably coupled to a shank 12 which supports theprobe in a head of a machine tool (not shown). The probe 10 has acylindrical housing 14 which terminates at the end of the probe adjacentthe shank in a radially extending annular lip 16 having an axiallyextending flange 18 defining an aperture 20. The end of the shank 12adjacent the probe 10 has a radially extending annular wall 22, whichdefines an aperture 23 and, (when the probe and shank are coupledtogether) receives the flange 18 with a clearance therebetween.

The probe 10 and shank 12 are coupled by means of a clamping mechanismwhich comprises clamping pin 24, having a head 26 and a shaft 28. Thepin 24 is movably engaged with the probe 10 by the head 26 which liesinside the probe housing 14 and bears against the lip 16. The shaft 28of the bolt projects through the aperture 20 into a cylindrical bore 30in the shank 12. The cylindrical bore 30 lies coaxially with the axis Aof the shank 12. The shaft 28 of the bolt has a diametric bore 32, and asubstantially cylindrical clamping element 34 is supported in the bore32 for radial movement with respect to the axis A. The clamping element34 is provided with a circumferential channel 36, and a ball bearing 38embedded in the surface of the bore 32 rests in the annular spacedefined by the surface of the bore 32 and the channel 36, thereby toretain the clamping element 34 within the bore 32. The clamping element34 has, at one end, an outwardly projecting conical clamping surface 40,and at the other end an inwardly projecting conical clamping surface 42.The surface 40 engages an inwardly projecting conical surface 44 in theend of a fixed clamping bolt 46 which lies in a diametrically extendingscrew threaded bore 48 in the body of the shank 12. Moveable clampingbolt 50 also lies in the screw threaded bore 48, and has an outwardlyprojecting conical surface 52 which engages the inwardly projectingsurface 42 of the element 34. The axis B of the element 34 lies closerto the wall 16 of the probe 10, than the axis C of the moveable clampingbolt.

To clamp the probe 10 and shank 12 together, the moveable clamping bolt50 is driven down the bore 48 toward the axis A of the shank 12, untilthe outwardly projecting surface 52 of the clamping bolt 50 comes intocontact with the inwardly projecting conical surface 42 of the clampingelement 34. Initially, the element 34 will be driven diametricallytoward the fixed clamping bolt 46. However, once clamping bolt 46 hasarrested the diametric movement of element 34, the action of outwardlyprojecting conical surface 52 on the inwardly projecting conical surface42 will result in an axial force acting on the shaft 28 of the pin 24 inthe direction of shank 12. This will force the head 26 against the innersurface of lip 16, and will clamp the probe and shank together.

Four adjusting bolts 54 are supported by the shank and project radiallythrough screw threaded bores 56 in the annular wall 22. The bolts 54bear against the outside of the flange 18, and adjustment of these bolts54 causes movement of the probe housing 14 relative to the shank 12 in aplane substantially orthogonal to the axis A. (The flange 18 thusprovides a shaft fixedly engaged with the probe against which theadjusting bolts may bear). When clamping the probe 10 and shank 12together, the preferred procedure is to tighten moveable clamping bolt50 until the clamping pin 24 retains the probe 10 and shank 12 togetherwith a pre-determined force, which is not sufficiently large to preventrelative lateral movement of probe 10 and shank 12, the relativeposition of the probe 10 and shank 12 is then adjusted with adjustingbolts 54, until the centre of the measuring tip 8 lies on the shank axisA. The adjustable clamping screw 50 is then tightened further until theprobe 10 and shank 12 are retained together with the desired force.

A second embodiment of a clamping assembly according to the presentinvention will now be described with reference to FIG. 3. A shank 60 hasa shaft 62 formed integrally with the shank at one end. A substantiallycylindrical probe body 68 terminates at one end in an annular flange 70,defining an axial bore 72. When the shank and probe body are engaged theshaft 62 projects into the bore 72.

As with the first embodiment, fixed and moveable clamping bolts 74 and76 respectively, lie in screw threaded bores 77 and 78 respectively. Aclamping element 80 is supported in a diametric bore in the shaft 62 forradial movement relative to the shaft 62, and one end of the clampingelement 80 has an outwardly projecting wedge 82 having two inclinedplane faces 83 which engage corresponding inwardly projecting planesurfaces 84 in the end of fixed clamping bolt 74. The other end ofclamping element 80 terminates in an inclined planar surface 88.Moveable clamping bolt 76 has an outwardly projecting conical surface90, which, as the bolt 76 is driven inwardly down the bore, engages thesurface 88. As described previously, the clamping element 80 willinitially move radially relative to the axis of shaft 62 until itsmotion has been arrested by virtue of its engagement with fixed clampingbolt 74. At this point, the action of moveable clamping bolt 76 oninclined surface 88 will draw the shaft 62 into the bore 72, therebyclamping the shank 60 and the probe body together.

In order to damp any vibration between the shank 60 and the probe body68, a spring mechanism 92 is provided. The mechanism 92 comprises asupporting ring 94 which lies around the circumference of shaft 62, anda belville washer 96 attached to the supporting ring 94. The belvillewasher 96 bears against a groove 97 in the inner surface of annular wall70.

Four adjusting bolts 98 are supported in radially extending screwthreaded bores (not shown) in the probe 68. The screws 98 bear againstthe shaft 62 and enable lateral adjustment of the shank relative to theprobe 68. The clamping procedure is as described in the firstembodiment.

A third embodiment of the present invention will now be described, withreference to FIG. 4.

Referring now to FIG. 4 a probe 100 has, at its rear face a shaft 102into which a retaining pin 104 is embedded. Both the shaft 102 and thepin 104 lie inside the retaining bore 106 in the taper shank 108. Theretaining pin 104 is sleeved by a clamping element in the form of acylindrical collar 110; the collar 110 sleeves the pin 104 sufficientlyloosely to allow relative movement of the pin 104 and collar 110perpendicular to the axis D of shank 108. The head 112 of the retainingpin 104 bears against the collar 110 via a Belleville washer 114. Thecollar 110 has a conical side face 116 and the largest diameter edge ofthe collar 110 fits closely into bore 106. The entire assembly of shaft102, pin 104, collar 110 and washer 114 comprises a projection whichlies inside the recess (in this case, a bore 106) provided in the shank108.

A clamping bolt 118 projects into the retaining bore 106, in a directionradial to the axis D. The end face of the clamping bolt 118 is conical,and bears against the concial face 116 of the collar 110. Since thelargest diameter of the collar 110 is adjacent the head 112 of the pin104, inward radial movement of the clamping bolt 118 will cause thecollar 110 to move away from the body of the probe 100, and thereforebear (via the Belleville washer 114) more strongly against the head 112of the pin 104. Thus, force applied to the collar by inward radialmovement of the bolt 118, produces a resultant clamping force whichclamps the taper shank 108 and the probe 100 together.

Radial adjustment of the relative alignment of the probe 100 and tapershank 108 is accomplished by means of four adjusting bolts 120, each ofwhich is supported in the body of the taper shank 108 and extendsradially into retaining bore 106 to bear against the shaft 102.

A coupling, and adjustment operation is thus performed as follows: theclamping bolt 118 is first tightened to cause the probe 100 to bearagainst the shank 108 with sufficient force to provide friction againstrelative radial movement of the two parts. The relative radial positionsof probe 100 and shank 108 are then adjusted using the four adjustingbolts 120. Once this has been completed, the clamping bolt 118 is fullytightened, thus drawing the probe 100 more firmly against the shank 108,without destroying the recently adjusted relative alignment of the twoparts.

A fourth embodiment of the present invention will now be described withreference to FIG. 5. A probe 140 terminates at its rear end in anannular lip 142. A clamping pin 144, having a head 146 and a shaft 148is moveably engaged with the probe 140 by virtue of its contact betweenthe head 146 and the lip 142. A shank 150 has a annular flange 152 whichextends into a hole 154 defined by the annular lip 142. The flange 152sleeves the shaft 148 of the pin 144, which extends into a bore 156 inthe shank 150. The shaft 148 has two mutually convergent frusto-conicalfaces 158, and a pair of clamping bolts 160, provided in diametricallyextending bores 162 each have a conical face 164, which bears againstthe frusto-conical surface remote from the probe 140. Inward radialmovement of one, or both the clamping bolts 160 will result in a forceon the shaft 148 in an axial direction, causing the head 146 of the pin144 to bear against the annular lip 142, and urge the probe 140 and theshank 150 together. Four radially extending, and equispaced adjustingbolts 166 extend in the annular lip 142, and bear against the flange 152of the shank 150, which thus provides a fixed shaft against which theadjusting bolts may bear. The method of adjustment using this embodimentof the present invention is as described for the previous embodiments.

As stated earlier, the provision of three or more adjusting screwsprevents relative movement of the tool and the shank (radially withrespect to each other) when the tool and the shank are being clampedaxially. Moreover, if the tool is to be used in conjunction with a toolchange apparatus which grasps the shank to remove the tool from amagazine and insert it into a spindle, then the continual jarring of thetool during changing may cause misalignment between the tool and theshank. The provision of three or more radially extending adjustingscrews helps to reduce this undesirable effect.

It is not essential that either of the shafts (i.e. the fixed shaftsprovided by the probe and shank as appropriate, and the moveable shaftsprovided by the clamping pins) be cylindrical. For example, it may bedesirable to provide square shafts, or triangular shafts (depending uponthe number of adjusting, and clamping bolts employed).

Typically, the touch probe illustrated in the embodiments of the presentinvention will be a touch trigger probe or an analogue touch probe. Ineither case, the stylus of the probe is supported on a stylus carrier,which is usually urged into a rest position with respect to the housingof the probe by a spring. The force required to displace the stylus fromthe said rest position is thus dependent directly upon the force withwhich the spring urges the stylus carrier into its rest position. It isocassionally desirable to adjust the spring force. However adjustment ofthe spring force in existing touch probes is possible only bydisengaging the probe from the shank. A third aspect of the presentinvention therefore provides means for adjusting the spring force of atouch probe while the probe is in situ (e.g. connected to a shank).

According to a third aspect of the present invention there is provided atouch probe having:

a housing;

a stylus carrier supported relative to the housing in a rest position;

a spring, extending in a first direction and having one end bearingagainst the stylus carrier, and another end bearing against an abutment;and

means actuable from a second direction lateral to the first direction,for adjusting the position of the abutment in the first direction.

Preferably, the abutment will comprise a clamping shuttle having anangled surface, so that a lateral adjusting force applied to the angledsurface will result in movement of the clamping shuttle perpendicular tothe applied force thus enabling adjustment of the position of theclamping shuttle in the first direction; such adjustment will cause achange in the degree of spring deformation and thus a change in thespring force.

The adjusting force will preferably be applied by a screw, having anangled surface at its bearing end for bearing against the angled surfaceof the clamping shuttle.

An example of such a touch probe will now be described with furtherreference to FIG. 5.

The stylus is supported in probe housing 141 on a stylus carrier 190,comprising a base 200, supported by three cylindrical rollers 202 whichextend equidistant to each other and radially to the axis E. When thestylus carrier is in its rest position, each of the rollers 202 seats ina cleft defined by an adjacent pair of steel balls 204 (of which onlyone is shown since the figure shows the stylus carrier in section). Thiskinematic arrangement is well-known, e.g. from U.S. Pat. No. 4,153,998,and therefore need not be described in more detail.

The stylus carrier is urged into its kinematic rest position by a springmechanism 206 comprising a spring 208 which bears against the base 200at one end via a conical member 210. The other end of the spring 208bears against an abutment in the form of a cylindrical clamping shuttle212 which is constrained to move in a bore 214. The free end of theclamping shuttle 212 terminates in a conical face 216. A radiallyextending bore 218 extends from the outer surface of the housing to thebore 214. The outer part of the radial bore 218 has a screw threadedpart 220 in which a radial adjusting screw 222 sits. The adjusting screw222 has at its inner end in a conical face 224, which bears against theconical face 216 of the clamping shuttle 212. Thus, adjustment of theradial adjusting screw 222 causes movement of the clamping shuttle 212along the bore 214, causing a change in the deformation of the spring208 and thereby causing a change in the spring force which urges thestylus carrier into its kinematic rest position. The extent of theinward radial movement of the radial adjusting screw 222 is constrainedby the countersunk seat 226.

We claim:
 1. An apparatus for use in a coordinate positioning machine,said apparatus comprising a tool and a shank, said shank retaining thetool in a spindle of the coordinate positioning machine, the tool andshank being clamped by a clamping mechanism, said apparatus comprising:abore provided in one of the tool and shank, the bore defining an axis; ashaft provided on the other of the tool and shank, the shaft projectinginto the bore and being movable in said bore in a direction transverseto said axis; a clamping element, supported on an end of the shaft formovement relative to the shaft in a direction transverse to said axis,the clamping element having a clamping surface inclined at an angle tosaid axis; means for providing sliding engagement of the clampingelement with the inside of the bore, thereby to enable movement of saidclamping element in said bore in an axial direction, and to preventmovement of said clamping element in said bore in a direction transverseto said axis; means provided on said one of the tool and shank forapplying a force to said clamping surface in a direction transverse tosaid axis thereby to generate a clamping force acting substantiallyparallel to said axis for clamping said tool to said shank; and meansfor adjusting the alignment of the tool and shank in a directiontransverse to said clamping force.
 2. The apparatus according to claim1, comprising a retaining pin connected to the end of the shaft, theretaining pin extending through an aperture provided in the clampingelement, wherein said aperture is sufficiently large to allow movementof the clamping element relative to the retaining pin in a directiontransverse to said axis.
 3. The apparatus according to claim 1, whereinsaid bore has a cylindrical cross-section and the clamping element has acylindrical outer surface which contacts the bore, thereby to providesaid sliding engagement.
 4. The apparatus according to claim 1, furthercomprising means for resiliently urging the clamping element intocontact with the end of the shaft.
 5. The apparatus according to claim1, comprising a plurality of adjusting bolts, provided on said one ofthe tool and shank, for bearing against said shaft.
 6. The apparatusaccording to claim 1, comprising a clamping bolt provided on said one ofthe tool and shank, extending transversely to said axis and bearingagainst said clamping surface.